The invention relates to an inductive winding suitable for use in a flat electric motor. A strip of an electrically insulating foil is subdivided into successive foil parts which are separated by folding lines and folded against each other along the folding lines. Each foil part has on at least one of its major surfaces an electrically conductive track which extends according to a curved line around an axis which is perpendicular to the major surfaces of the foil parts. The conductor tracks are electrically connected together by means of connection tracks, the curved lines followed by the conductor tracks on the foil parts being meander-like with a number of curves connected by connection members. The curves cooperate with the connection tracks and the connection members to form coils arranged in a circle around the axis.
Such a winding is known from FR-A No. 1 376 322. The known winding may comprise a large number of turns formed by cooperation of the conductor tracks and connected together by the connection tracks. The conductor tracks and the connection tracks are provided in one operation in a manner conventionaly used in the manufacture of printed circuits, and connections between parts of the winding need not be made afterwards by soldering or a similar operation. The winding can therefore be manufactured easily and at low cost.
The rotor or the stator of a flat electric motor generally has the form of an approximately circular disc having a central aperture. The known method of manufacturing windings from a foil with conductor tracks has the drawback that before or after folding the shape of the packet has to be adapted by cutting away the corners and punching the central part. These are extra operations which in addition produce loss of material. It is an object of the invention to provide a winding of the kind set forth which can be manufactured substantially without loss of material and without any extra after-treatments. To achieve this, the winding in accordance with the invention is characterized in that the long sides of the foil strip are crenellated so that the strip comprises a succession of wide and narrow rectangles and that the folding lines, viewed in the longitudinal direction of the strip, extend alternately from one long side of the strip to the other, and conversely, each folding line extending from a corner point of a narrow rectangle present on one of the long sides to a corner point of the next narrow rectangle present on the oppositely located long side so that the foil parts have the form of parts of an octagon having a central aperture. This winding has an octagonal outer circumference and a square aperture in the center, with which the desired shape proves to have been approached sufficiently for practical purposes.